This application corresponds to Netherlands patent application Nos. 7602078, filed Feb. 28, 1976, and 7609526, filed Aug. 27, 1976, the disclosure of which is hereby incorporated by reference.
It is known that phenols can be prepared by treating a substituted or unsubstituted benzoic acid compound such as the acid or a salt, ester or anhydride thereof in the liquid phase and at an elevated temperature, with a molecular oxygen containing gas in the presence of a copper catalyst dissolved in the reaction mixture. The term "phenol" as used in this application includes both hydroxybenzene and ring substituted derivatives thereof. For example, the following phenol products can be prepared by this process from the indicated benzoic acid compound:
______________________________________ Acid Starting Material Phenol Product ______________________________________ Benzoic acid Phenol 2-Methylbenzoic acid 3-Hydroxytoluene 3-Methylbenzoic acid 2- and 4-Hydroxytoluene 4-Methylbenzoic acid 3-Hydroxytoluene 3-Nitrobenzoic acid 4-Nitrophenol 4-Nitrobenzoic acid 3-Nitrophenol 4-Chlorobenzoic acid 3-Chlorophenol and Phenol 4-Biphenylcarboxylic acid 3-Hydroxybiphenyl 2,4-Dimethylbenzoic acid 2,5-Dimethylphenol ______________________________________
See Hydrocarbon Processing, volume 43, pages 173 ff. (November 1965), which is hereby incorporated by reference. In this process of producing a phenol (as defined above), a tar-like product is also formed which until our invention has not been useful. Thus, until our invention it was customary to burn this tar-like product. In addition to being wasteful, this tar-like product often contained residues of the copper catalyst used. When the tar-like product was burned, the copper catalyst residues were sent into the atmosphere as copper oxides, etc., along with the combustion gases. Obviously, this is an environmental hazard, and costly equipment was necessary to remove the copper oxides from the combustion gases. Thus, in the practice of the prior art process not only was the tar-like product wasted, but copper catalyst itself was burned up, and costly equipment was required to remove the oxidized copper catalyst from the combustion gases.